Due to the highly developed pore structure and extremely large specific surface area of activated carbon, its application developed from decolorization and deodorization for food and medicine, gas masks, to large-scale use in solvent refining and recycling, advanced water treatment, flue gas purification and blood purification etc. The development has brought new and higher requirements on the properties such as adsorption and strength of activated carbon.
In addition, in the production of activated carbon, the method of preparing coal-based activated carbon using coal as raw material has been widely used. In order to make the obtained activated carbon have higher strength when used, usually, it is necessary to carry out a briquetting treatment before the coal is carbonized and activated. Therefore, high-strength briquetting of coal is also the basis for the preparation of high-strength activated carbon.
Although pulverized coal briquetting technologies have been widely used in the deep processing of raw coal, various binders such as coal pitch still need to be added in most pulverized coal briquetting technologies, which not only increases the cost, but also the prepared coal briquettes need to be air-dried or heated and roasted, thereby reducing the production efficiency; in addition, since the commonly used binders such as coal pitch and coal tar will melt and volatilize after being heated, so that the strength of the final product is not high, and in the production of activated carbon, residues such as coal pitch will block the pores of activated carbon, some residues also contain harmful substances, which is not conducive to improving the quality of activated carbon, thus limiting the application of non-caking coal in the preparation of coal-based activated carbon.
At present, the research on the preparation of binder-free, coal-based activated carbon has become a hot topic. CN101402454A discloses a preparation method of formed activated carbon, wherein pulverized coal is subjected to press forming before being activated by carbonization, however, in order not to add a binder, a large amount of weak caking coal and strong caking rich coal have to be added to the pulverized coal raw material. Due to the addition of a large amount of caking coal, it is necessary to slowly increase the temperature during the carbonization process to prevent the particles from foaming and coking during the carbonization process, and a long activation time is required to make the obtained activated carbon have a large enough surface area.
CN1033262A discloses a method for preparing activated carbon comprising pulverizing non-caking coal to below 10 μm and then subjecting the pulverized coal to press forming. It is stated in this patent application that the smaller the particle size after pulverization of raw coal, the more advantageous it is to increase the number of contact points per unit weight between the particles to increase the adhesion between the sub-particles in the particles. However, the smaller the particle size after pulverization of pulverized coal, the greater the possibility of agglomeration. Considering the requirement of moisture in subsequent press forming, moisture control is difficult, and pulverization is also difficult, requirements to equipments are high and the method is difficult to popularize. At the same time, studies found that too fine particle size of pulverized coal tends to cause the internal pores to be too fine after briquetting, affecting the escape of subsequent carbonized volatiles and the diffusion of gas used for activation into internal pores when activated carbon is prepared, and thus affecting the yield and adsorption of the final product.
Therefore, it is necessary to propose a new preparation method for binder-free, coal-based, briquetted activated carbon.